Conventionally, a Fiber Reinforced Plastic (FRP), which is a material made by reinforcing resin with fibers such as a carbon fiber and a glass fiber is broadly applicable to aircrafts, railroads, automobiles, and the like, because of its higher strength and lower weight compared to metals. As a resin for manufacturing a high-strength FRP, typically a thermosetting resin is used.
FRP is manufactured by various methods. For example, high-quality Carbon Fiber Reinforced Plastic (CFRP) components used for aircrafts are manufactured by autoclave molding using prepreg.
Also, there are RTM (Resin Transfer Molding) that fibers are arranged in a mold cavity and resin is pressed thereinto, and VaRTM (Vacuum Assisted Resin Transfer Molding) that injection pressure is performed only by a vacuum pressure. The rest are a hand lay-up method and a spray-up method as manufacturing methods for small-lot production of wider-ranging products, and SMC (Sheet Molding Compound) as a manufacturing method for mass production.
FRP has a feature that it not only has higher strength and lower weight compared to metals but also can realize a complicated shape relatively easily. This is because a mold is used when molding FRP, and an aerodynamically excellent shape can be easily applied to a molded article by the die.
A typical example that FRP is applied is a case that a front bodyshell of a front car of an high-speed railcar is manufactured with FRP. When the front bodyshell of the front car is manufactured not with FRP but with metal materials, an external plate such as a bent aluminum plate is welded on a frame assembled in a grid shape by welding. At this time, it is difficult to obtain a predetermined shape due to a thermal deformation in welding. Although there is also a method of cutting and shaping the front bodyshell from a block material such as aluminum by machining, material loss becomes large. In contrast, when using FRP, as a complicated shape is easily molded using the mold as mentioned above, manufacturing cost can be reduced.
Also, when a desired rigidity cannot be obtained with a single FRP, a sandwich structure that a FRP 20 is laminated on a core material 21 is made as illustrated in FIG. 7. Typically, a honeycomb core or a resin foam can be given as the core material 21. As the front bodyshell of the front car of the high-speed railcar to which the above-mentioned FRP is applied is required to be light and highly rigid, it has a sandwich structure. While travelling, birds or the like collide with the front bodyshell of the front car and the honeycomb core leads to compression (buckling) failure. Therefore, a resin foam (foamed core material) is used as a core material (see PTL 1). However, the foamed core material is required not to break due to an external force by the load upon a bird strike.